1. Field of the Invention
This invention relates to a semiconductor device.
2. Description of the Related Art
Development of SiC semiconductor element using SiC (silicon carbide) has been promoted in recent years.
The SiC semiconductor element has attracted public attention as a power device that controls large electric power, by virtue of its higher breakdown field than that of Si semiconductor element, and its wider band gap. The SiC semiconductor element can operate at temperatures as high as 150° C. or above at which Si semiconductor element cannot endure, and is reportedly operable even at 500° C. or above on the theoretical basis (see JP-A-2011-80796).
By the way, the semiconductor elements are used in the form of semiconductor device while housed in a case for protection, and sealed by a sealing layer that is composed of a resin sealing material filled up in the case.
At present, the sealing layer composed of a resin sealing material is durable only in the temperature range up to 150° C., and can degrade and produce therein a void above 150° C. where the SiC semiconductor element can operate. This is disadvantageous in terms of keeping the semiconductor device durable enough.
There has therefore been no choice but to use the SiC semiconductor element so that the operating temperature will not exceed the heat resistance temperature
of the sealing layer, and this has prevented the SiC semiconductor element from fully demonstrating the performances.
Such SiC semiconductor element has been used as a power device in a booster circuit for boosting DC voltage; or in a power changing circuit such as an inverter circuit for changing DC voltage into AC voltage, and a converter circuit for changing AC voltage into DC voltage.
For example, railway vehicles include those supplied with DC power for running and those supplied with AC power for running. Both of them have an inverter for controlling AC power to be fed to a traveling motor, and for this inverter, the power device is used.
Since, as described above, the heat resistant temperature of the sealing layer made of a resin sealing material is as high as 150° C. or below at present, so that the power device for the inverter, when operated at above 150° C. as the railway vehicle travels, tends to break down due to degradation of the sealing layer.
Most of recent railway vehicle accidents are caused by such failure of the power device due to degradation of the sealing layer under elevated operating temperature. Repair of the power device needs a great deal of labor and cost. The situation therefore needs some improvement.
This sort of failure of the power device under elevated operating temperature has also occurred in electric vehicles having the inverter for driving a traveling motor, or in power generating facilities using the inverter for changing solar-generated DC power into utility AC power, and has been desired to be improved.
Meanwhile, in JP-B1-5281188 granted to the present applicant, there have been proposed insulating materials excellent in physical/chemical strength.